Electrical indicator



May 29, 195.6 K. c. HUDSON ELECTRICAL INDICATOR Filed sept.. so, 1954 FI G. 4

F I G.

FIG. 3

INVENTOR. KENNETH C. HUDSON ATTORNEY.

I 5 l/ l n United States 2,748,231 Patented VMay 29, 195.6

ELECTRICAL INDICATOR Kenneth Clifford Hudson, Philadelphia, Pa.,assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.,a corporation of Delaware Application September 30, 1954, Serial No.459,315

15 Claims. (Cl. 201--55) A general object of the present invention is toprovide a new and improved form of electrical resistance element. Morespecifically, the invention is concerned with an improved variableresistance element of the type utilizing an electrically conductivefluid to variably shunt a resistance coating on the wall of a hollowtube wherein the hysteresis error due to meniscus variations of thefluid in the element is minimized.

When a variable resistor is formed by coating the inner surface of ahollow tube with resistance material and the coating is shunted by ashort circuiting fluid, it has been found that a dead spot will appearin the apparatus due to the shape of the meniscus of the iluid changing.The meniscus shape change is accompanied by volume change of the fluid,in the vicinity of the coating which is shorted by the Huid, without anychange in the point at which the tluid contacts the resistance material.The present invention is directed to the elimination of this dead spotin resistance units of the present type by maintaining the meniscus ofthe iluid in a substantially constant shape even though the tluid levelmay change within the resistance unit.

It is therefore a more specific object of the present invention toprovide means for regulating the meniscus shape of a fluid used in avariable resistance unit of the present type.

Another object of the present invention is to provide a uid meniscuscontrol for use in a variable resistance wherein the control element isin the form of a nonwettable rod which extends into the fluid.

In some forms of the present invention, it is desired not only toregulate or control the meniscus of the fluid used, but also to vary thelevel of the uid in the tube. Adjustment of the tluid level may beaccomplished by varying the depth to which the meniscus control elementextends into the fluid.

Another object of the invention is then to provide an improved form ofadjustable element for the uid level in the resistance unit used in thepresent apparatus.

A further object of the invention is to provide an improved resistanceelement including a movable meniscus control element which may bevariably extended into the uid of the resistance unit to regulate theiluid level of the unit.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its advantages, and specific objects attained with its use, referenceshould be had to the accompanying drawings and descriptive matter inwhich there is illustrated and described preferred embodiments of theinvention.

Of the drawings:

Fig. l is a representative showing of the variable resistance unitconnected to a recording instrument;

Fig. 2 shows an enlarged cross section of a resistance unit of the typeused in the present invention wherein no meniscus control is utilized;

Fig. 3 shows an enlarged cross sectional detail of a portion of Fig. 1wherein a meniscus control element is used;

Fig. 4 shows a modified form of the present invention wherein themeniscus control rod is adjustable in the amount that it extends intothe iluid of the unit; and

Fig. 5 shows one manner in which the meniscus control rod of the presentinvention may be characterized to provide a non-linear response of theresistance unit to uid level changes as effected either by the movementof the rod or other movement.

Referring rst to Fig. l, the numeral 10 represents a thermometer bulbwhich may be filled with mercury or some other suitable thermallyexpansible material having electrical short circuiting properties. Thebulb 10 has formed on the upper portion thereof a glass or ceramic typeof capillary tubing 1l. The tubing il has a resistance coating 12 formedon the inner portion thereof. Contacting the coating at either endthereof are a pair of contacts 13 and 14. As explained thus far, theunit is substantially the same as that disclosed in the copendingapplication of Edward F. Zoltanski, Serial No. 290,601, tiled May 28,1952.

Centered within the hollow portion of the tube -11 is a meniscus controlelement 15. This element is fastened at the upper end of the tube il atlo and at the lower end of the tube lll at 18. The meniscus controlelement 15 is preferably formed of a non-wettable material such asquartz or tungsten. The type of material selected depends upon the fluidor liquid used in the device. it has been found that quartz and tungstenare very effective when used with mercury.

Connected to the output terminals of the resistance unit is a suitableindicating and recording instrument 20. This instrument may well takethe form of the instrument disclosed in the patent to Walter P. Wills,No. 2,423,540, issued July 8, 1947.

In considering the operation of Fig. l, temperature changes of the bulb10 are accompanied by a resultant expansion or contraction of themercury which fills the bulb. The level of the mercury will accordinglyrise and fall over the resistance coating 12 so that the coating will bevariably short circuited or shunted by the mercury and the resistancebetween the output contacts i3 and 14 will change. This change may bereilected into the instrument 20 which will give an appropriateindication of the magnitude of the resistance. While a thermal bulb l0has been shown, it will be readily apparent that any suitable means forinducing the flow of the fluid in the tube 11 may be employed within theteachings of the present invention.

Fig. 2 shows the mercury meniscus change resulting from some forceacting upon the column of mercury to cause a movement thereof. The solidline 25 over the mercury column 9 represents the normal meniscus shapeto be expected inside of the tube 11. The edges of the mercury contactsthe resistance coating 12 at 26. lf the mercury column 9 is subjected toa force tending to move it in an upward direction, the meniscus levelwill change in an upward direction and take the shape of a dotted linecurve 27 before the edge of mercury in Contact with the surface l2 willleave the contact point 2o. if there is a decrease in the force actingon the column 9, the column will be lowered and will assume the shapeidentified by the dotted line curve 28 before the edge of the mercurycolumn 9 will depart from the contact point 26.

It will be readily apparent from a consideration of Fig. 2 that theremay be a considerable change in'the volume of the mercury column 9 inthe vicinity of the resistance coating l2 without any accompanyingchang:k in the contact point of the mercury with the resistance coating.This volume change appears as an apparent dead 'spot in the operation ofthe sensing unit. For precision measurement purposes, such a dead spotis intolerable.

As is shown in enlarged detail on Fig. 3, the appa ratus of Fig. lovercomes the shortcomings present in the apparatus of the typerepresented in Fig. 2. Added to the apparatus shown in Fig. 2 is themeniscus control rod 15 which may be formed of quartz, tungsten, or someother suitable non-wetting material. With a meniscus control rod lpresent within the tube li, the shape of the meniscus Will remainsubstantially that as shown regardless of whether the uid level isincreasing or decreasing in its position within the tube l1.Consequently, the dead spot area present within the apparatus issubstantially eliminated. It has been found that the most eectivediameter for the meniscus control rod should be at least one tenth theinside diameter of the tubing 11.

An additional advantage has been observed in the addition of themeniscus control rod to the apparatus in respect to eliminating gasbubbles which may be formed below the normal level of the mercury byseparation of the mercury in the tube 11. With the arrangement disclosedand including the control rod l5, gentle tapping upon the tube has beenfound sufficient to cause the bubbles or separations to be eliminated sothat the mercury column is solid all the way down into the bulb 10.

In the modication of Fig. 4, the meniscus control rod is made adjustableso as to facilitate ready adjustment of the level of the mercury withinthe resistance element. There is provided in this modication a hollowtube 3i) having a resistance coating 31 on the inner surface. Fillingthe lower portion of the tube 30 is a suitable shunting liquid 32 suchas mercury which is adapted to move over the resistance coating 31 andvariably short the same. A pair of contacts 33 and 34 are displaced onopposite ends of the resistance coating 31 and provide output terminalsfor the apparatus. Fastened to the upper end of the tube 30 is a chamber35 of enlarged cross section. Separating the chamber 35 from the tube 30is a threaded portion 36 which is adapted to threadedly receive ameniscns control rod 37, the latter having a projection 38 which extendsdown into the mercury 32. The upper end of the rod 37 has fastenedthereto a permanent magnet 39 which is adapted to cooperate with apermanent magnet assembly 40 disposed outside of the chamber 35. Themagnetic assembly 4t) may be rotatably adjustable by the gearing dsl-42.

In operation, the tube 30 and the coperating elements may form avariable resistance which is varied solely by the movement of the rod 37with extension 38 varying the level of the mercury 32 upon theresistance coating 31. The extension 38 of the rod 37 serves themeniscus control function of the rod of Fig. l. When the gearing 41-42is rotated, the magnets 40 follow the gear 41 and the permanent magnet39 will follow the magnet 40 so as to rotate the rod 37 and vary thedepth to which the extension 38 extends into the mercury 32. This formof the apparatus may well be used for establishing a predeterminedresistance change for a certain input angular motion.

In the event that it is desired to provide a zero adjustment forapparatus of the type shown in Fig. l, the principles incorporated inFig. 4 may well be substituted in the apparatus of Fig. l.

In some instances, it is desired to provide a non-linear responsebetween liquid motion and the resistance change of the coating. For thispurpose, the non-linear element or rod 45, shown in Fig. 5 may Well besubstituted for the rod 37 and its extension 38. The rod 4S willfunction as a meniscus control element as well as a means forintroducing a non-linear response in the apparatus.

While, in accordance with the provisions of the statutes, there has beenillustrated and described the best forms of embodiment of the inventionknown, it will be apparent .to those skilled in the art that changes maybe `made in the forms of the apparatus disclosed without departing fromthe spirit of the invention as set forth in the appended claims, andthat in some cases certain features of the invention may be used toadvantage without a corresponding use of other features.

Having now described the invention, what is claimed as new and for whichit is desired to secure Letters Patent is:

l. A variable electrical resistance device comprising a ceramiccapillary tube having an electrically conducting but resistive coatingpositioned on the inner surface of the capillary, electrical contactingmeans positioned at spaced points along said capillary and engaging saidcoating, an electrically conducting iluid having a negligible electricalresistance disposed in cooperative relation with said coating tovariably shunt the electrical resistance of said coating between saidpoints, and an elongated element supported within and extendingcoaxially along the length of said capillary tube, said element having across sectional diameter less than that of the inner portion of saidtube.

2. Apparatus as dened in claim l wherein said elongated element is notwettable by said fluid so that said element acts to control the meniscuslevel of said fluid in said tube.

3. Apparatus as defined in claim 2 wherein said elongated element isformed of tungsten.

4. Apparatus as defined in claim 2 gated element is formed of quartz.

5. An electrical resistor comprising a hollow tube having anelectrically conducting but resistive coating formed on the innerportion of said tube, an electrically conducting liuid having negligibleelectrical resistance disposed relative to said coating to variablyshunt the electrical resistance of said coating7 and a fluid meniscuscontrol element extending into said iluid to maintain the meniscusthereof of substantially constant shape when said fluid variably shuntssaid coating.

6. A variable resistance element comprising a hollow tube having anelectrically conducting but resistive coating formed on the innerportion of said tube, an electrically conductive uid having negligibleelectrical resistance disposed in variable shunting relation withrespect to said resistive coating, an elongated rod extending along thelength of said tube and into said liuid, and means for adjusting thelength of said rod extending into said liuid to vary the level of theHuid acting on said coating.

7. Apparatus as defined in claim 6 wherein said rod has a non linearcharacterization so that movement thereof will produce a non linearchange in level of the uid acting on said coating.

8. Apparatus as defined in claim 6 wherein said elongated rod is formedof a substance which is not wettable by said fluid.

9. Apparatus as dened in claim 8 wherein said rod is formed of quartz.

l0. Apparatus as delined in claim 8 wherein said rod is formed oftungsten.

ll. A variable resistance element comprising a hollow tube having anelectrically conducting but resistive coating formed on the innerportion of said tube, an electrically conductive uid having negligibleelectrical resistance disposed in variable shunting relation withrespect to said resistive coating, an elongated rod extending along thelength of said tube and into said fluid, means threadedly supportingsaid rod in said tube, and means for rotating said rod in said supportto variably position said rod in said fluid.

l2. Apparatus as defined in claim l1 wherein said means for rotatingsaid rod comprises a magnetic coupling including a magnetic memberinside of said tube on said rod and a second magnetic member outside ofsaid tube mounted for rotational movement.

wherein said elon- 13. Apparatus as dened in claim 7 wherein saidelongated rod is formed of a substance which is not Wettable by saiduid.

14. Apparatus as defined in claim 7 wherein said rod is formed ofquartz.

15. Apparatus as defined in claim 7 wherein said rod is formed oftungsten.

References Cited in the le of this patent UNITED STATES PATENTS

